a. Field of the Invention
This invention relates to a novel preparation process of 4,4'-biphenol. More particularly, it relates to a novel preparation process of 4,4'-biphenol from 4-(4-hydroxyphenyl)-3-cyclohexene-1-ol and to a novel compound 4-(4-hydroxyphenyl)-3-cyclohexene-1-ol which can be utilized as a precursor of 4,4'-biphenol.
4,4'-Biphenol is useful as a stabilizer, an intermediate of dyestuffs and a material for preparing resins such as polyesters, polyepoxides, polyurethanes and polycarbonates. Much attention has particularly been focused on this compound in recent years as a material for high-temperature resistant resins.
b. Description of the Prior Art
A variety of processes have been proposed to date for the preparation of 4,4'-biphenol. 4,4'-Biphenol was first prepared by the diazo decomposition of benzidine (Chemische Berichte, 22, 335). Thereafter it was prepared by the alkali fusion of sodium 4,4'-biphenyldisulfonate [U.S. Pat. No. 2,368,361 (1942)]. In recent years, processes for obtaining biphenol by the dealkylation of tetra-tert-butyldiphenol which is derived from 2,6-di-tert-butylphenol [J. of Organic Chemistry, 34, 1160 (1969), and other sources] have been fully researched. Many patents were applied for using this process. In addition, a process by the dehalogenation and dimerization of halogenated phenols (Japanese Laid-Open Patent No. 53631/1981), and a process by the alkali treatment of dihalogenated biphenyl (Japanese Laid-Open Patent No. 22347/1979) are known. Various other processes have also been proposed these conventional processes, however, have such disadvantages as toxicity, the high cost of raw materials, problems with the disposal of waste water, severe reaction conditions and low yields.
Since the present inventors succeeded in obtaining a novel compound of 4,4-bis(4-hydroxyphenyl)cyclohexanol by the reaction of 4-hydroxycyclohexanone with phenol in the presence of a catalyst, a process for obtaining 4,4'-biphenol by the decomposition and dehydrogenation reaction of above novel compound was previously proposed (Japanese Patent Application No. 144734/1986). The process, however, carried out the decomposition reaction of 4,4-bis(4-hydroxyphenyl)cyclohexanol and successive dehydrogenation reaction in one step and was not always satisfactory from the industrial standpoint.
In other words, in the decomposition-dehydrogenation reaction of 4,4-bis(4-hydroxyphenyl)cyclohexanol, the generation of by-products, e.g., mainly p-phenylphenol, is inevitable and the 4,4'-biphenol usually contains more than 10% of p-phenylphenol.
Since 4,4'-biphenol has a high boiling point and a high melting point and there is few good solvents for it, it is difficult to separate by-products such as p-phenylphenol. In particular, in using 4,4'-biphenol as a monomer for polymerization, p-phenylphenol should be removed in order to prevent its action as a polymerization terminator. A remarkable amount of 4,4'-biphenol is lost during the removal of p-phenylphenol.
Therefore it is particularly necessary to inhibit the formation of p-phenylphenol as much as possible during the reaction. Conventional processes, however, are limited in the inhibition of by-products such as p-phenylphenol and have not always been satisfactory.